This invention relates to an automatic welding process and its computer-assisted welding system. This computer-assisted welding system, or CAW system, makes it possible to control the welding process in real time.
The invention finds its applications in many fields and, more particularly, in the so-called "high technology" industries, such as the nuclear, aeronautics, space and farm-produce fields.
Today, most welding operations require the continual proximity of a human operator to face unexpected conditions. Actually, in production operation, the welding conditions are rarely totally constant; they generally exhibit random and unforeseen disturbances, such as deformations, irregularities, deviations of position, etc. These disturbances often have unfortunate consequences on the quality of the welding.
However, automatic welding devices exist that take into account certain of these disturbances. These devices are listed in a work titled "Robots de soudage, capteurs et adaptativite de trajectoire" ["Welding Robots, Sensors and Path Adaptivity"], published in 1988 by HERMES publishers, under the signature of J. M. DETRICHE.
Most of these devices exist in the form of sensors retrofitted to previously existing installations. Thus, most of these devices assure checking only of a single function of the welding process, this function very often being the tracking of the welding joint.
This invention makes it possible precisely to control a large part of the functions of the welding process, and this in real time.
The welding process according to the invention assures a self-checking of the CAW system, which consequently makes it possible to perform welds under conditions that cannot be controlled by a human operator (speed, precision, efficiency) in a hostile environment.
The CAW system according to the invention comprises in particular a welding head which comprises a device for imaging the welding scene in progress. The images thus obtained are processed in real time by a processing and control means (for example, a computer) so as to deduce from them the values of the possible corrections to be made to the system to obtain an even, quality weld. This system uses an automatic welding process based on a learning from the welding cases already processed.
More specifically, the CAW welding process consists in a first stage of prior establishment of a methodical and quantitative knowledge of the laws of behavior of the material during a welding operation. This knowledge is expressed by relationships between the various welding parameters.
According to the invention, the relationships comprise relationships connecting a measured parameter with a result parameter, as well as relationships connecting a result parameter with a controllable parameter.
These three parameters interact, each result parameter being subject to an appropriate constant value, by correction of the controllable parameter from the determination of the measured parameter.
Advantageously, the establishment of these relationships consists in establishing a data base from triplets of parameters each comprising a measured parameter, a controllable parameter and a result parameter.
These relationships can comprise, among others, and for different welding conditions, relationships between the welding current and the length of the molten bath in operation and the geometric parameters of the resultant welding bead.
In the same way, they can also comprise relationships between the welding current and the contour of the molten bath in operation and the geometric parameters of the resultant bead.
The relationships necessary for the slaved operation of the CAW system are then installed in said system, either in software form, or in hardware form.
During the physical production of a weld in CAW mode, the CAW process consists in carrying out a second stage comprising the following operations:
a) taking of pictures of a welding scene in progress; PA1 b) analysis of this picture-taking to measure the necessary parameters; PA1 c) calculation, from these measurements and from said relationships reinstalled in the system, of the correction values to be made to the welding parameters during the execution of the welding; PA1 d) intervention on the welding parameters. PA1 a welding head; PA1 a carrier (or, more precisely, a welding bench) to which the welding head is fastened; PA1 means for supplying the head with voltage; PA1 a processing and control unit (PCU) connected to the welding head and to the bench. PA1 the welding head comprises means for taking pictures of the welding scene; PA1 the welding bench is able to be moved relative to the welding scene; and PA1 the processing and control unit (PCU) comprises a central processing unit (CPU), means for analyzing the pictures and means for controlling the power supply means and the welding bench.
Advantageously, it comprises between operations (a) and (b) a dialog operation with a user assuring a choice of automatic execution or interactive execution of operations (b) to (d).
For a continuous checking of the welding, operations (a) to (d) are continuously repeated as long as an interrupt order has not been received. This interrupt order is given by the user during the interactive dialog operation.
Moreover, picture-taking operation (a) is optionally followed by an operation of storing said pictures on a video recorder, for example.
In ordinary operation, picture-taking operation (a) consists in taking said pictures in a continuous mode. However, in the case of selecting interactive execution, the user can also give the order to take said pictures in a shot-by-shot mode, for parametering needs for example.
Such a process can be applied in a CAW system. The system using this process comprises:
This system is characterized by the fact that:
Advantageously, the processing and control unit further comprises means for displaying the images and means for storing said images, located upstream from the analysis means.
Moreover, the means for analyzing the images of the welding scene comprises an image acquisition card installed in the CPU, this card being connected to the means for displaying the images and to the means for storing the images.
According to the invention, the central processing unit comprises input/output interface cards able to establish connections between the CPU and the welding bench, between the CPU and the power supply means and between the CPU and the welding head.
More particularly, the voltage supply means comprises a welding generator comprising two inputs, the first receiving a nominal current value and the second receiving a current value of correction to be made to said nominal current. These nominal and correction current values can be controlled from the CPU.
In addition, the system further comprises a means for regulating an arc voltage that is connected, at input, to the welding head, and, at output, to the welding bench.